118 
LIFE, IN ITS LOWER FORMS. 
ened point, the very extremity of which is perforated, 
forming a mouth through which the juices of the animal- 
tissue are absorbed into the sac. Here, then, are indubi- 
table characteristics of a living independent being. Here 
is a stomachal cavity in which foreign matter is assimi- 
lated, and this is imbibed through a distinct mouth. 
But more ; a provision is needed for the attachment of 
the parasite while it is thus drawing its nutriment, and this 
is given in a twofold mode. First, around the sides of 
the extremity of the lengthened neck are placed four oval 
suckers, adapted for adhering to a smooth surface ; and, 
secondly, around the oval aperture there is a double circle 
of minute recurved hooks, which, fixing into the snrround- 
ing flesh, anchor the mouth securely, while, at the same 
time, by the irritation which they produce, they cause the 
vital juices to flow more abundantly to the wounded part, 
and thus increase the sustenance of the parasite. 
Other forms differ from this chiefly in the increased 
number of their organs ; the bladder, for instance, is fur- 
nished with many such heads, as in that species which in- 
fests the brain of sheep ; or the head, if single, is a pro- 
trusile proboscis, armed with many rows of recurved 
spines j or, if there be but one head, and that armed with 
but two rows of hooks and one series of suckers, the neck 
is greatly developed and divided into a great number of 
segments, while the bladder is diminished to a compara- 
tively small swelling at the hinder extremity. 
We are thus brought to consider that horrible pest, the 
Tape-worm ( Tania), which consists of a ribbon-like body, 
formed of square flattened segments, sometimes amounting 
to five hundred in number, and attaining an aggregate 
